Method and system for secure key rotation

ABSTRACT

This invention discloses a novel system for securing and using payment token data in a system for processing electronic payment transactions that does not require down-time for rekeying encryption keys when the keys are rotated.

FIELD OF INVENTION

The present invention generally relates to the field of credit card andelectronic payment security.

BACKGROUND

Electronic payment systems rely on data encryption in order to securethe data tokens used by consumers and merchants to authorize payment.Credit card numbers are particularly sensitive data because a completecard number, and its attendant data, can be submitted by anyone forpurchase. Similarly, any other kind of payment authorization tokensuffers the same vulnerability. At the same time, merchants operatingcomputerized sales transaction systems have a need to store thissensitive data for periods of time. In some cases, the customer agreesthat the merchant can store the credit card in order that consumer enjoythe convenience of not re-entering the numbers into their browserinterface operating on their computer. Industry best practices dictatethat storage of credit card numbers and any other type of paymentauthorization token be secured by means of encrypting the data. However,encryption simply shifts the data security vulnerability from the dataitself (which is now encrypted) to the security of the keys. Onesolution is that the data encryption keys (DEK) be changed periodically.During that process, all of the encrypted data needs to be re-keyed.This means that the system's day to day business operation is suspendedwhile new encryption keys are generated and each encrypted data item inthe payment token database is decrypted with the old key andre-encrypted with the new one. This process, commonly referred to as keyrotation and re-keying can cause disruption of business operations.

Therefore, there is a need for a key rotation mechanism that permits theelectronic transaction to continue to operate during the key rotationand re-keying process. These and other objects, features andcharacteristics of the present invention will become more apparent tothose skilled in the art from a study of the following detaileddescription in conjunction with the appended claims and drawings, all ofwhich form a part of this specification. It should be understood thatthe description and specific examples are intended for purposes ofillustration only and not intended to limit the scope of the presentdisclosure.

DESCRIPTION OF THE FIGURES

The headings provided herein are for convenience only and do notnecessarily affect the scope or meaning of the claimed invention. In thedrawings, the same reference numbers and any acronyms identify elementsor acts with the same or similar structure or functionality for ease ofunderstanding and convenience. To easily identify the discussion of anyparticular element or act, the most significant digit or digits in areference number refer to the Figure number in which that element isfirst introduced (e.g., element 204 is first introduced and discussedwith respect to FIG. 2).

FIG. 1. System components.

FIG. 2. Transaction Server adapted for rendering encrypted card data

FIG. 3. Transaction Server adapted for storing encrypted pan data

FIG. 4. Rekeying Server process.

FIG. 5. AddCard process.

FIG. 6. InfoCard vault process.

FIG. 7. Update card vault process.

FIG. 8. Embodiment of database storage.

FIG. 9. Key Rotation process states.

FIG. 10. User interface flow.

DETAILED DESCRIPTION

Various examples of the invention will now be described. The followingdescription provides specific details for a thorough understanding andenabling description of these examples. One skilled in the relevant artwill understand, however, that the invention may be practiced withoutmany of these details. Likewise, one skilled in the relevant art willalso understand that the invention can include many other features notdescribed in detail herein. Additionally, some well-known structures orfunctions may not be shown or described in detail below, so as to avoidunnecessarily obscuring the relevant description. The terminology usedbelow is to be interpreted in its broadest reasonable manner, eventhough it is being used in conjunction with a detailed description ofcertain specific examples of the invention. Indeed, certain terms mayeven be emphasized below; however, any terminology intended to beinterpreted in any restricted manner will be overtly and specificallydefined as such in this Detailed Description section.

The system is comprised of a card vault component, which containsencrypted information about customers, including payment information.Referring to FIG. 1, the customer information, which includes thePrimary Account Number (PAN) is input into the system. The PAN can be acredit card number. The PAN can also be any other alphanumeric stringrepresenting an authorization for payment. In one embodiment, the PANvalues for customers are stored in a database with other relatedcustomer data, the PAN database or PAN table. The PAN values are onlystored after they are encrypted. In one embodiment, the PAN values areencrypted twice, one with a first data encryption key (DEK1) and theother with a second data encryption key (DEK2). Both versions of theencrypted PAN value are stored in the database. The database may beorganized as a table, and then referred to as the PAN table. In thissystem, another database stores the data encryption keys, or DEKs. Thedata encryption keys themselves are stored in encrypted form, usinganother key called the Key Encryption Key or KEK. The DEKs are stored ina database, typically in the form of a table, or DEK table, thatassociates the encrypted DEK with an identifier or DEK ID.

In a typical key rotation, the entries in the DEK table will be changedso that the existing first DEK or DEK1 is prepared to be discarded, thekey DEK2 remains and a new DEK, or DEK3 is generated, encrypted with theKEK and inserted into the table with its new DEK ID. The object ofrekeying is so that the PAN data that is encrypted with the DEK1 key isdecrypted first before the DEK1 key is discarded and then re-encryptedwith the new DEK key, referred to here as DEK3. The prior art rekeyingoperation entails stopping all transactions while the system decryptseach PAN entry in the PAN table and re-encrypts it with the new DEK3,and inserts that value into the PAN table. After the rekeying, the PANtable contains two entries for the encrypted PAN, one using the DEK2encryption key and the DEK3 encryption key. After re-keying, the DEK1key entries may be discarded.

One embodiment of the invention where a system is adapted to process theDEK keys so that key rotation and rekeying can occur while the system isstill processing payment transactions. FIG. 2 depicts a transactionserver component of the system adapted for the process of getCard, forfetching the encrypted payment token, for example, a credit card number,from the database and decrypting it. In this embodiment, the two DEKkeys which when stored in the database in encrypted form, are decryptedbut only stored in the data memory of the servers that are processingtransactions. This is so that the process of fetching a DEK ID, anencrypted DEK and KEK from the DEK table database does not need to beperformed on each transaction, which slows the entire system down. Otherembodiments include storing the unencrypted DEKs in the CPU stack, CPUregisters, cache memory, main memory or other memory that is not readilyaccessible by other systems or processes other than the CPU of theserver itself operating an authorized process. The decrypted DEKs storedin memory are also locally stored with their corresponding DEK IDs.

In this embodiment, the latest two DEK IDs for the currently used DEKsare fetched from the DEK table. The fetched DEK IDs are used to checkwhether the pair matches the DEK IDs of the decrypted DEKs stored inmemory. If the pair of DEK IDs does not match the pair of DEK IDs inmemory, then the current two DEKs are fetched from the database,decrypted with the KEK and updated in memory. In some cases, one of thetwo DEKs retrieved is simply the overlapping DEK that already resides inmemory, which occurs during a key rotation. However, in that case, whereone of the two DEK IDs, match, then the system can fetch the PAN recordfrom the card vault database with the latest or highest DEK ID, e.g.DEK3. That PAN record will also include the entry corresponding to theDEK ID that is one generation older, e.g. DEK2. This condition occurswhen the DEK3 has been generated and is in the process of rekeying intothe PAN database. Nonetheless, the DEK2 entry is still valid and may beused by the transaction server to decrypt the PAN and process thetransaction. The validity is determined because the DEK ID for DEK2 inmemory matches the DEK ID in the DEK table. The decrypted DEK2, which isalready in memory, can be used to complete the transaction. Thiscondition, where the DEK2 is still usable and the DEK3 has not beenplaced in main memory, can continue until the DEK ID for DEK2 is notused anymore, that is, upon the next key rotation, which case the priorcondition, no DEK IDs matching, requires the transaction server to fetchthe new keys from the database.

Another embodiment of the system has a component adapted so that thesystem can accept a payment token, for example, a card number input by auser and insert that into the PAN database or table. FIG. 3 shows theprocess, further described as follows. The server fetches the latest twoDEK IDs from the database. It then tests for the condition whether thepair of DEK IDs stored in memory matches the DEK IDs retrieved from thedatabase. If not, the two DEKs are fetched and decrypted and the memorylocations updated. However, if they do match, that step is skipped.Control flow thereby arrives at the step of encrypting the paymenttoken, or PAN entry, and storing the result in the respective PAN tableentry with the DEK ID and Initialization Vector (IV) value for the CardVault Key that was used. In this step, the system generates a random IVto be used for the encryption of the PAN, and the result is encryptedwith the clear DEK present in memory. With this system component, thesystem can continue to accept payment tokens and enter them into the PANusing the two DEKs in memory. During rekeying, the overlapping key, e.g.the DEK 2 is still present. The DEK3 entries into the PAN will beupdated by means of a separate re-keying process operating independentlyof the transaction server. This embodiment allows a user to enter newcards in the system regardless of the rekeying state. With thisembodiment, the end result is all new entries in the system will bestored encrypted with the latest two DEK IDs such that one of the DEKIDs will be an overlap from the previous generation DEK IDs and the newgeneration of DEK IDs. During the rekeying process, if this card vaultrecord has a PAN entry with the latest DEK ID, it will be skipped.However, if it doesn't, it will be picked up so that the oldest DEK fromthe last generation keys is rekeyed with the latest DEK ID in thesystem.

The system is also comprised of an administration server that is adaptedto process the rekeying component of the system independently of thetransaction servers. This component of the system systematically updatesthe PAN table entries using the new DEK3 and DEK3 ID. FIG. 4 shows thesystem component adapted for rekeying. The system fetches the latestthree DEKs from the DEK table and decrypts them with the KEK. The newgenerated DEK ID and the last two from the previous generation of DEKIDs. The decrypted values are stored in the memory of the rekeyingserver. The server marches through the card vault database looking forPAN entries where the PAN record does not have a DEK ID that matches thelatest DEK ID, that is, the DEK ID for DEK3. If the result of this queryis not null, then for each of these card vault entries, the older DEK1is used to decrypt the PAN entry corresponding to DEK ID for DEK 1. Thenthis data is re-encrypted using DEK3 and re-stored into the database.This process continues until the database query returns a “null”, whichmeans the rekeying is complete. An important aspect of the system isthat the next DEK in line for rotation and rekeying, e.g. DEK 2, cannotbe rotated until the rekeying process is complete.

Practitioners of ordinary skill will recognize that the components ofthe system can be embodied as separate processes operating on physicallyseparate servers as well as different processes operating on the samephysical servers in various combinations. In the typical system, thetransaction servers and administration server components may beprocesses operating on the same physical hardware, but the card vaultdatabase and the DEK database may be physically distinct.

Operating Environment:

The system is typically comprised of a central server that is connectedby a data network to other computers. The central server may becomprised of one or more computers connected to one or more mass storagedevices. The precise architecture of the central server does not limitthe claimed invention. In addition, the data network may operate withseveral levels, such that the user's computer is connected through afire wall to one server, which routes communications to another serverthat executes the disclosed methods. The precise details of the datanetwork architecture does not limit the claimed invention.

A server may be a computer comprised of a central processing unit with amass storage device and a network connection. In addition a server caninclude multiple of such computers connected together with a datanetwork or other data transfer connection, or, multiple computers on anetwork with network accessed storage, in a manner that provides suchfunctionality as a group. Further, a server may be virtual, wherebyseveral software instances each operating as an independent server arehoused in the same hardware computer. Practitioners of ordinary skillwill recognize that functions that are accomplished on one server may bepartitioned and accomplished on multiple servers that are operativelyconnected by a computer network by means of appropriate inter processcommunication. In addition, the access of the website can be by means ofan Internet browser accessing a secure or public page or by means of aclient program running on a local computer that is connected over acomputer network to the server. A data message and data upload ordownload can be delivered over the Internet using typical protocols,including TCP/IP, HTTP, SMTP, RPC, FTP or other kinds of datacommunication protocols that permit processes running on two remotecomputers to exchange information by means of digital networkcommunication. As a result a data message can be a data packettransmitted from or received by a computer containing a destinationnetwork address, a destination process or application identifier, anddata values that can be parsed at the destination computer located atthe destination network address by the destination application in orderthat the relevant data values are extracted and used by the destinationapplication.

The system and method described herein can be executed using a computersystem. The system may be comprised of one or more components, eachgenerally comprised of a central processing unit (CPU) that isoperatively connected to a memory device, data input and outputcircuitry (I/O) and computer data network communication circuitry. Avideo display device may be operatively connected through the I/Ocircuitry to the CPU. Components that are operatively connected to theCPU using the I/O circuitry include microphones, for digitally recordingsound, and video camera, for digitally recording images or video. Audioand video may be recorded simultaneously as an audio visual recording.The I/O circuitry can also be operatively connected to an audioloudspeaker in order to render digital audio data into audible sound.Audio and video may be rendered through the loudspeaker and displaydevice separately or in combination. Computer code executed by the CPUcan take data received by the data communication circuitry and store itin the memory device. In addition, the CPU can take data from the I/Ocircuitry and store it in the memory device. Further, the CPU can takedata from a memory device and output it through the I/O circuitry or thedata communication circuitry. The data stored in memory may be furtherrecalled from the memory device, further processed or modified by theCPU in the manner described herein and restored in the same memorydevice or a different memory device operatively connected to the CPUincluding by means of the data network circuitry. The memory device canbe any kind of data storage circuit or magnetic storage or opticaldevice, including a hard disk, optical disk or solid state memory.

The computer can display on the display screen operatively connected tothe I/O circuitry the appearance of a user interface. Various shapes,text and other graphical forms are displayed on the screen as a resultof the computer generating data that causes the pixels comprising thedisplay screen to take on various colors and shades. The user interfacealso displays a graphical object referred to in the art as a cursor. Theobject's location on the display indicates to the user a selection ofanother object on the screen. The cursor may be moved by the user bymeans of another device connected by I/O circuitry to the computer. Thisdevice detects certain physical motions of the user, for example, theposition of the hand on a flat surface or the position of a finger on aflat surface. Such devices may be referred to in the art as a mouse or atrack pad. In some embodiments, the display screen itself can act as atrackpad by sensing the presence and position of one or more fingers onthe surface of the display screen. When the cursor is located over agraphical object that appears to be a button or switch, the user canactuate the button or switch by engaging a physical switch on the mouseor trackpad or computer device or tapping the trackpad or touchsensitive display. When the computer detects that the physical switchhas been engaged (or that the tapping of the track pad or touchsensitive screen has occurred), it takes the apparent location of thecursor (or in the case of a touch sensitive screen, the detectedposition of the finger) on the screen and executes the processassociated with that location. As an example, not intended to limit thebreadth of the disclosed invention, a graphical object that appears tobe a 2 dimensional box with the word “enter” within it may be displayedon the screen. If the computer detects that the switch has been engagedwhile the cursor location (or finger location for a touch sensitivescreen) was within the boundaries of a graphical object, for example,the displayed box, the computer will execute the process associated withthe “enter” command. In this way, graphical objects on the screen createa user interface that permits the user to control the processesoperating on the computer.

The invention may also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotecomputer storage media including memory storage devices. Practitionersof ordinary skill will recognize that the invention may be executed onone or more computer processors that are linked using a data network,including, for example, the Internet. In another embodiment, differentsteps of the process can be executed by one or more computers andstorage devices geographically separated by connected by a data networkin a manner so that they operate together to execute the process steps.In one embodiment, a user's computer can run an application that causesthe user's computer to transmit a stream of one or more data packetsacross a data network to a second computer, referred to here as aserver. The server, in turn, may be connected to one or more mass datastorage devices where the database is stored. The server can execute aprogram that receives the transmitted packet and interpret thetransmitted data packets in order to extract database query information.The server can then execute the remaining steps of the invention bymeans of accessing the mass storage devices to derive the desired resultof the query. Alternatively, the server can transmit the queryinformation to another computer that is connected to the mass storagedevices, and that computer can execute the invention to derive thedesired result. The result can then be transmitted back to the user'scomputer by means of another stream of one or more data packetsappropriately addressed to the user's computer.

Computer program logic implementing all or part of the functionalitypreviously described herein may be embodied in various forms, including,but in no way limited to, a source code form, a computer executableform, and various intermediate forms (e.g., forms generated by anassembler, compiler, linker, or locator.) Source code may include aseries of computer program instructions implemented in any of variousprogramming languages (e.g., an object code, an assembly language, or ahigh-level language such as FORTRAN, C, C++, JAVA, or HTML or scriptinglanguages that are executed by Internet web-browsers or nativelyexecuted by local applications or apps) for use with various operatingsystems or operating environments. The source code may define and usevarious data structures and communication messages. The source code maybe in a computer executable form (e.g., via an interpreter), or thesource code may be converted (e.g., via a translator, assembler, orcompiler) into a computer executable form.

The invention may be described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computer. Generally, program modules include routines,programs, objects, components, data structures, etc., that performparticular tasks or implement particular abstract data types. Thecomputer program and data may be fixed in any form (e.g., source codeform, computer executable form, or an intermediate form) eitherpermanently or transitorily in a tangible storage medium, such as asemiconductor memory device (e.g., a RAM, ROM, PROM, EEPROM, orFlash-Programmable RAM), a magnetic memory device (e.g., a diskette orfixed hard disk), an optical memory device (e.g., a CD-ROM or DVD), a PCcard (e.g., PCMCIA card), or other memory device. The computer programand data may be fixed in any form in a signal that is transmittable to acomputer using any of various communication technologies, including, butin no way limited to, analog technologies, digital technologies, opticaltechnologies, wireless technologies, networking technologies, andinternetworking technologies. The computer program and data may bedistributed in any form as a removable storage medium with accompanyingprinted or electronic documentation (e.g., shrink wrapped software or amagnetic tape), preloaded with a computer system (e.g., on system ROM orfixed disk), or distributed from a server or electronic bulletin boardover the communication system (e.g., the Internet or World Wide Web.) Itis appreciated that any of the software components of the presentinvention may, if desired, be implemented in ROM (read-only memory)form. The software components may, generally, be implemented inhardware, if desired, using conventional techniques.

The described embodiments of the invention are intended to be exemplaryand numerous variations and modifications will be apparent to thoseskilled in the art. All such variations and modifications are intendedto be within the scope of the present invention as defined in theappended claims. Although the present invention has been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only, and is not to be taken by wayof limitation. It is appreciated that various features of the inventionwhich are, for clarity, described in the context of separate embodimentsmay also be provided in combination in a single embodiment. Conversely,various features of the invention which are, for brevity, described inthe context of a single embodiment may also be provided separately or inany suitable combination. It is appreciated that the particularembodiment described in the specification is intended only to provide anextremely detailed disclosure of the present invention and is notintended to be limiting.

It should be noted that the flow diagrams are used herein to demonstratevarious aspects of the invention, and should not be construed to limitthe present invention to any particular logic flow or logicimplementation. The described logic may be partitioned into differentlogic blocks (e.g., programs, modules, functions, or subroutines)without changing the overall results or otherwise departing from thetrue scope of the invention. Oftentimes, logic elements may be added,modified, omitted, performed in a different order, or implemented usingdifferent logic constructs (e.g., logic gates, looping primitives,conditional logic, and other logic constructs) without changing theoverall results or otherwise departing from the true scope of theinvention.

Also, while processes or blocks are at times shown as being performed inseries, these processes or blocks may instead be performed orimplemented in parallel, or may be performed at different times.

What is claimed:
 1. A system for processing electronic purchasetransactions comprising: a transaction server comprised of memoryfurther comprised of first and second stored decryption keys, each ofthe first and second decryption keys corresponding to first and secondkey identifiers also stored in memory, the server further adapted toreceive second and third decryption key identifiers; receive a datarecord comprised of two entries, each entry the same payment tokenencrypted by encryption keys corresponding to the second and thirddecryption key identifiers, where the first, second and third keyidentifiers are distinct and the first, second and third decryption keysare distinct; selecting from the received data record one of the twoencrypted payment token entries that corresponds to the seconddecryption key identifier; and decrypting the selected entry using thesecond decryption key residing in memory.
 2. The system of claim 1further comprising: an additional transaction server comprised of memorycomprised of first and second stored encryption keys, each of the firstand second encryption keys corresponding to first and second keyidentifiers also stored in memory, the additional transaction serveradapted to receive a payment token; receive second and third keyidentifiers; encrypt the payment token with the encryption keyassociated with the second key identifier; input the encrypted paymenttoken into a data record corresponding the payment token, said entryfurther corresponding to the second key identifier, where the first,second and third key identifiers are distinct and the first, second andthird encryption keys are distinct.
 3. An additional transaction servercomprised of memory comprised of first and second stored encryptionkeys, each of the first and second encryption keys corresponding tofirst and second key identifiers also stored in memory, the additionaltransaction server adapted to receive a payment token; receive secondand third key identifiers; determine whether the first key identifierdoes not match the third key identifier, and in dependence thereon,retrieve the an encryption key associated with the third key identifier;encrypt the payment token with the encryption keys associated with thesecond and third key identifiers; input the encrypted payment token intoa data record corresponding the payment token, said entry furthercorresponding to the second key identifier and third identifier wherethe first, second and third key identifiers are distinct and the first,second and third encryption keys are distinct.
 4. A system forprocessing electronic purchase transactions comprising: a transactionserver comprised of memory comprised of first and second storeddecryption keys, each of the first and second decryption keyscorresponding to first and second key identifiers also stored in memory,the server further adapted to receive third and fourth key identifiers;receive a data record comprised of two entries, each entry the samepayment token encrypted by third and fourth encryption keys, each keycorresponding to the third and fourth key identifiers; determine whichof the third or fourth key identifiers match the first or second keyidentifiers; select one of the two encrypted payment token entries thatcorresponds to the matched key identifier; and decrypt the selectedentry using the decryption key residing in memory corresponding to thematched key identifier.
 5. The system of claim 3 where the transactionserver is further adapted to determine if neither the first nor secondkey identifiers match either the third or fourth key identifiers, and independence thereon, request and receive encrypted forms of third andfourth decryption keys corresponding to the third and fourth keyidentifiers and decrypting the received third and fourth decryptionkeys.
 6. The system of claim 3 further comprising a rekeying server, therekeying server adapted to retrieve first and second key identifiersfrom a key database, the first key identifier being the latest keyidentifier of the first and second keys; request from a database a datarecord comprised of two entries, each entry the same payment tokenencrypted by encryption keys corresponding to third and fourth keyidentifiers, the third key being the latest key of the third and fourthkeys; determining whether the pair of third and fourth key identifiersfail to match the pair of first and second key identifiers, and independence on such determination, decrypting the entry corresponding tothe fourth key identifier and re-encrypting the entry using theencryption key corresponding to the first key identifier.
 7. The systemof claim 5 further adapted to prevent a new key rotation until thesystem detects the condition that the request step returns a nullresult.
 8. A system for operating electronic payment of transactionscomprising: A transaction server comprised of a means for payment tokendecryption and a means for payment token encryption.
 9. The system ofclaim 6 further comprising a server comprised of a means for rekeyingencrypted payment tokens.
 10. The system of claim 8 where the rekeyingmeans is adapted to prevent a new key rotation until the rekeying of theencrypted payment tokens is complete.